Influence of reactive sputter deposition conditions on crystallization of zirconium oxide thin films

Zirconium oxide thin films were prepared through reactive magnetron sputtering with a zirconium target using pulsed-dc and radio frequency (rf) sources. The film crystallization was studied with respect to sputtering growth variables such as sputtering power, sputtering pressure, source frequency, oxygen pressure, substrate temperature, and substrate material. The crystallization was studied through x-ray diffraction (XRD) 2θ scans and was quantified with peak full width at half maximum and crystallite size. Crystallization of the films was found to occur over a broad range of sputter deposition parameters, while the amorphous phase was produced only at high sputtering pressure and low sputtering power. With a decrease in sputtering pressure or power, the crystallite size decreased. Energy dispersive x-ray spectroscopy, electron microscopy, and XRD analysis revealed that at very low pressures, these films are polyphase assemblages of cubic phases of oxygen deficient zirconium oxides such as ZrO and Zr2O. When the sputtering oxygen content of these films is increased above 25%, monoclinic-ZrO2 phase is stabilized in the films and the deposition rate decreases. However, in the case of rf sputtering, an additional peak corresponding to tetragonal phase of ZrO2 is observed. The sputtering parameters were related to physical parameters such as sputtering mode, ion energy, and substrate temperature, which influence crystallinity.